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Chinese researchers have created fertile live mouse pups by reprogramming skin cells into powerful stem cells.

Dr Fanyi Zeng of the Shanghai Institute of Medical Genetics at Shanghai Jiao Tong University, and colleagues, report their findings today online ahead of print publication in the journal Nature.

The researchers created whole mice using induced pluripotent skin cells, or iPS cells, which were reprogrammed to look and act like embryonic stem cells.

The mice went on to have babies, the first of which has been called Xiao Xiao, or Tiny, say the researchers.

Their experiment means that it is theoretically possible to clone someone using skin cells, but the experts have been quick to distance themselves from such controversy.

"We are confident that tremendous good can come from demonstrating the versatility of reprogrammed cells in mice, and this research will be used to," says Zeng.

"This gives us hope for future therapeutic interventions, using the patient's own reprogrammed cells in the far future," she says.

"It would not be ethical to attempt to use iPS cells in human reproduction. It is important for science to have ethical boundaries … [the study was] in no way meant as a first step in that direction".

The rise of iPS cells

Stem cells are the body's master cells, giving rise to all the tissues, organs and blood.

Embryonic stem cells are considered the most powerful kind of stem cells as they have the potential to give rise to any type of tissue.

But they are difficult to make and require the use of an embryo or cloning technology. Many people also object to using human embryonic stem cells and many countries limit funding for such experiments.

In 2006 and 2007 Dr Shinya Yamanaka of Kyoto University introduced four genes into skin cells, reprogramming them so that they became indistinguishable from embryonic stem cells - these famously versatile iPS cells can develop into almost any type of tissue.

That achievement conjured the allure of an almost limitless source of transplant material that would be free of the same controversy associated with embryonic stem cells.

But until now, no-one has been able to prove that iPS cells are as versatile as embryonic stem cells.

Fertile mice offspring

To demonstrate the pluripotency of the iPS cells, the Chinese researchers injected them into a tetraploid blastocyst, a group of cells that can only become placental tissue.

The scientists created 37 iPS stem cell lines, and of these, three generated live births.

"One line can generate such competent mice that the longest living one we have is nine months," says Zeng.

"It has generated now more than 100 of second-generation [mice] and more than 100 third-generation [mice]. It really demonstrates how fertile and strong the system is."

Questions raised

Independently, another group of researchers in China also report in the journal Cell Stem Cell that they have created whole mice from iPS cells.

The two Chinese experiments have generated questions and caution from other stem cell researchers not connected to the studies.

"The research reported in these two papers independently and formally demonstrates, using the most stringent test available, that mouse iPS cells are capable of forming an entire mouse," says Dr Andrew Laslett, from the Australian Stem Cell Centre in Melbourne.

"[But] the long term stability of both the iPS cell lines and the long term health of the mice generated using this procedure are yet to be reported."

Professor Andrew Elefanty of Monash Immunology and Stem Cell Laboratories in Melbourne notes only a small proportion of the iPS lines worked, "indicating that the reprogramming process was not entirely complete or normal."

"The bottom line is that this is a proof that some iPS lines can be 'completely' reprogrammed but that there is still a lot to learn about making the process efficient and safe," says Elefanty.

"These iPS cell lines carried reprogramming viruses in them that we know predispose to tumours."